3.1 INTRODUCTION

The objective of this chapter is to introduce the concept of radar cross section and the fundamentals of electromagnetic scattering in an overview fashion so that the reader may then delve into the remainder of the book. The topics to be presented are

• Terms: The definition of radar cross section from IEEE, an intuitive derivation, the polarization scattering matrix for linear polarization and its conversion to circular polarization, and the definition of total cross section and extinction cross section and the forward scattering theorem;

• Fundamental physical processes of electromagnetic scattering: Electromagnetic wave fundamentals, induced charges and currents, field lines attached to charges, near, intermediate and far fields, solenoidal and conservative fields, and the concepts for scattered, incident, and total field;

• Scattering regimes: The low-frequency Rayleigh region with induced-dipolelike scattering, the resonant region with attached surface wave scattering; and the high-frequency optics region with the concepts of individual scattering centers; opticslike specular, end-region, and diffraction scattering mechanisms; phasor addition as how various scattering mechanisms sum to form a total scattered field; and the concepts for coherent and incoherent sums of individual scattering centers;

• Electromagnetic theory: Field quantities and their sources; Maxwell s equations in differential and integral form; vector and scalar potentials as sources for solenoidal and conservative field components; wave equation and characteristic solutions; waves at boundaries; reflection, transmission, and absorption coefficients; Fresnel reflection coefficients; EM wave formalism compared to transmission line theory; surface current point of view; and the Stratton-Chu integral equation formulation...